Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/3217
20170428T14:14:03Z

Axisymmetric photonic structures with PTsymmetry
http://hdl.handle.net/2117/102467
Axisymmetric photonic structures with PTsymmetry
Ahmed Waseem, Waqas Waseem; Herrero Simon, Ramon; Botey Cumella, Muriel; Staliunas, Kestutis
PTsymmetric structures in photonic crystals, combining refractive index and gainloss modulations is becoming a research field with increasing interest due to the light directionality induced by these particular potentials. Here, we consider PTsymmetric potentials with axial symmetry to direct light to the crystal central point obtaining a localization effect. The axial and PTsymmetric potential intrinsically generates an exceptional central point in the photonic crystal by the merge of both symmetries. This particular point in the crystal lattice causes field amplitude gradients with exponential slopes around the crystal center. The field localization strongly depends on the phase of the central point and on the complex amplitude of the PTpotential.
The presented work analyzes in a first stage 1D linear PTaxisymmetric crystals and the role of the central point phase that determines the defect character, i.e. refractive index defect, gainloss defect or a combination of both. The interplay of the directional light effect induced by the PTsymmetry and the light localization around the central point through the axial symmetry enhances localization and allows higher field concentration for certain phases. The linearity of the studied crystals introduces an exponential growth of the field that mainly depends on the complex amplitude of the potential. The work is completed by the analysis of 2D PTaxisymmetric potentials showing different spatial slopes and growth rates caused by symmetry reasons.
Copyright 2016 Society of PhotoOptical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.
20170314T17:19:20Z
Ahmed Waseem, Waqas Waseem
Herrero Simon, Ramon
Botey Cumella, Muriel
Staliunas, Kestutis
PTsymmetric structures in photonic crystals, combining refractive index and gainloss modulations is becoming a research field with increasing interest due to the light directionality induced by these particular potentials. Here, we consider PTsymmetric potentials with axial symmetry to direct light to the crystal central point obtaining a localization effect. The axial and PTsymmetric potential intrinsically generates an exceptional central point in the photonic crystal by the merge of both symmetries. This particular point in the crystal lattice causes field amplitude gradients with exponential slopes around the crystal center. The field localization strongly depends on the phase of the central point and on the complex amplitude of the PTpotential.
The presented work analyzes in a first stage 1D linear PTaxisymmetric crystals and the role of the central point phase that determines the defect character, i.e. refractive index defect, gainloss defect or a combination of both. The interplay of the directional light effect induced by the PTsymmetry and the light localization around the central point through the axial symmetry enhances localization and allows higher field concentration for certain phases. The linearity of the studied crystals introduces an exponential growth of the field that mainly depends on the complex amplitude of the potential. The work is completed by the analysis of 2D PTaxisymmetric potentials showing different spatial slopes and growth rates caused by symmetry reasons.

Predictability of optical rogue waves in optically injected semiconductor lasers
http://hdl.handle.net/2117/101604
Predictability of optical rogue waves in optically injected semiconductor lasers
Martinez Alvarez, Nuria; Reinoso, Jose A.; Masoller Alonso, Cristina
The predictability of ultrahigh pulses emitted by optically injected semiconductor lasers is studied by using symbolic timeseries analysis. Pulse patterns that are likely to occur before the rogue wave are identified.
20170227T10:14:31Z
Martinez Alvarez, Nuria
Reinoso, Jose A.
Masoller Alonso, Cristina
The predictability of ultrahigh pulses emitted by optically injected semiconductor lasers is studied by using symbolic timeseries analysis. Pulse patterns that are likely to occur before the rogue wave are identified.

Slow light enabled wavelength demultiplexing
http://hdl.handle.net/2117/100768
Slow light enabled wavelength demultiplexing
Hayran, Zeki; Turduev, M.; Botey Cumella, Muriel; Herrero Simon, Ramon; Staliunas, Kestutis; Kurt, H.
Photonic crystal waveguides supporting band gap guided modes hold great potential to tailor the group
velocity of propagating light. We propose and explore different wavelength demultiplexer design approaches that utilize
slow light concept. By altering the dielectric filling factors of each waveguide segment, one can show that different
frequencies can be separated and extracted at different locations along the cascaded waveguide. Furthermore, to
eliminate the inherent reflection loss of such a design, a composite structure involving a tapered waveguide with a
sidecoupled resonator is also presented. Such a structure features not only a forward propagating wave but also a
backward propagating wave acting as a feedback mechanism for the drop channels. We show that by careful design of
the waveguide and the resonator, the destructive and instructive interference of these waves can effectively eliminate
the reflection loss and increase the coupling efficiency, respectively. Numerical and experimental verification of the
proposed structures show that the targeted frequencies can be coupled out with low crosstalks and moderate quality
factors, while maintaining a compact size. © 2016 IEEE.
20170209T13:54:56Z
Hayran, Zeki
Turduev, M.
Botey Cumella, Muriel
Herrero Simon, Ramon
Staliunas, Kestutis
Kurt, H.
Photonic crystal waveguides supporting band gap guided modes hold great potential to tailor the group
velocity of propagating light. We propose and explore different wavelength demultiplexer design approaches that utilize
slow light concept. By altering the dielectric filling factors of each waveguide segment, one can show that different
frequencies can be separated and extracted at different locations along the cascaded waveguide. Furthermore, to
eliminate the inherent reflection loss of such a design, a composite structure involving a tapered waveguide with a
sidecoupled resonator is also presented. Such a structure features not only a forward propagating wave but also a
backward propagating wave acting as a feedback mechanism for the drop channels. We show that by careful design of
the waveguide and the resonator, the destructive and instructive interference of these waves can effectively eliminate
the reflection loss and increase the coupling efficiency, respectively. Numerical and experimental verification of the
proposed structures show that the targeted frequencies can be coupled out with low crosstalks and moderate quality
factors, while maintaining a compact size. © 2016 IEEE.

PTaxisymmetric photonic nanostructures
http://hdl.handle.net/2117/90240
PTaxisymmetric photonic nanostructures
Ahmed Waseem, Waqas Waseem; Botey Cumella, Muriel; Herrero Simon, Ramon; Staliunas, Kestutis
Optical ParityTime (PT) symmetric systems support unusual properties. When the symmetric coupling between internal modes is broken the system becomes strongly unidirectional resulting in novel effects such as asymmetric reflections, invisibility or asymmetric mode coupling. Here, we propose a new class of nanophotonic PTaxisymmetric systems which lead to an extreme field enhancement and high localization at the Psymmetry center when the coupling of inward propagating waves is favored due to the asymmetric radial coupling. We expect the effect to have direct applications such as rendering broad aperture lasers into bright and narrow output beam sources.
20160927T13:50:04Z
Ahmed Waseem, Waqas Waseem
Botey Cumella, Muriel
Herrero Simon, Ramon
Staliunas, Kestutis
Optical ParityTime (PT) symmetric systems support unusual properties. When the symmetric coupling between internal modes is broken the system becomes strongly unidirectional resulting in novel effects such as asymmetric reflections, invisibility or asymmetric mode coupling. Here, we propose a new class of nanophotonic PTaxisymmetric systems which lead to an extreme field enhancement and high localization at the Psymmetry center when the coupling of inward propagating waves is favored due to the asymmetric radial coupling. We expect the effect to have direct applications such as rendering broad aperture lasers into bright and narrow output beam sources.

Tunable wavelengthdemultiplexer by tapered photonic crystal waveguide
http://hdl.handle.net/2117/85665
Tunable wavelengthdemultiplexer by tapered photonic crystal waveguide
Hayran, Zeki; Turduev, Mirbek; Botey Cumella, Muriel; Herrero Simon, Ramon; Staliunas, Kestutis; Kurt, H.
We numerically investigate the design of a wavelength demultiplexer based on a tapered photonic crystal waveguide. The tapered waveguide is generated by reducing the width of the channel which, in turn, provides a gradual change in the effective index for the guided modes. Depending on the wavelength, the grading effect enables the propagating beam to be trapped at different spatial positions along the waveguide. Furthermore, alternation on the tapering angle, i.e. changing the slope of the tapered waveguide, will result in a spatial shifting of the trapping locations. Thus, the structure can be adjusted to pick up the frequencies of interest at the chosen positions. Numerical results show that, by placing vertical line defects as drop channels at specific locations, different wavelengths can be properly guided along the drop channels that are transverse to the main waveguide.
20160414T11:57:27Z
Hayran, Zeki
Turduev, Mirbek
Botey Cumella, Muriel
Herrero Simon, Ramon
Staliunas, Kestutis
Kurt, H.
We numerically investigate the design of a wavelength demultiplexer based on a tapered photonic crystal waveguide. The tapered waveguide is generated by reducing the width of the channel which, in turn, provides a gradual change in the effective index for the guided modes. Depending on the wavelength, the grading effect enables the propagating beam to be trapped at different spatial positions along the waveguide. Furthermore, alternation on the tapering angle, i.e. changing the slope of the tapered waveguide, will result in a spatial shifting of the trapping locations. Thus, the structure can be adjusted to pick up the frequencies of interest at the chosen positions. Numerical results show that, by placing vertical line defects as drop channels at specific locations, different wavelengths can be properly guided along the drop channels that are transverse to the main waveguide.

Stimulus induced resonance in a neural mass model driven with a temporally correlated noise
http://hdl.handle.net/2117/85442
Stimulus induced resonance in a neural mass model driven with a temporally correlated noise
Jedynak, Maciej; Pons Rivero, Antonio Javier; García Ojalvo, Jordi
20160408T14:43:13Z
Jedynak, Maciej
Pons Rivero, Antonio Javier
García Ojalvo, Jordi

Ultrashort pulse chirp determination via transverse autocorrelation in SBN crystal
http://hdl.handle.net/2117/84721
Ultrashort pulse chirp determination via transverse autocorrelation in SBN crystal
Wang, Bingxia; Cojocaru, Crina; Inigo Sola, Inigo Sola; Wieslaw Krolikowski, Wieslaw Krolikowski; Yan Sheng, Yan Sheng; Vilaseca Alavedra, Ramon; Trull Silvestre, José Francisco
We determine the different initial chirp parameters of ultrashort pulses down to 30 fs via singleshot transverse autocorrelation method based on transverse second harmonic generation in SBN crystal with random distribution of inverted nonlinear domains. With the measured chirp and time duration parameters, we simulate the transverse autocorrelation traces and the corresponding pulse time duration evolutions, which have a good match with the experimental results
20160318T15:19:16Z
Wang, Bingxia
Cojocaru, Crina
Inigo Sola, Inigo Sola
Wieslaw Krolikowski, Wieslaw Krolikowski
Yan Sheng, Yan Sheng
Vilaseca Alavedra, Ramon
Trull Silvestre, José Francisco
We determine the different initial chirp parameters of ultrashort pulses down to 30 fs via singleshot transverse autocorrelation method based on transverse second harmonic generation in SBN crystal with random distribution of inverted nonlinear domains. With the measured chirp and time duration parameters, we simulate the transverse autocorrelation traces and the corresponding pulse time duration evolutions, which have a good match with the experimental results

Asymmetric light transmission by using 2D PTsymmetric photonic nanostructure
http://hdl.handle.net/2117/76340
Asymmetric light transmission by using 2D PTsymmetric photonic nanostructure
Turduev, M.; Botey Cumella, Muriel; Herrero Simon, Ramon; Kurt, H.; Staliunas, Kestutis; Giden, I.
We propose for the first time a simple realization of a twodimensional ParityTime symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an antisymmetric gain/loss distribution on the same scale. That leads to nonreciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.
20150727T11:42:50Z
Turduev, M.
Botey Cumella, Muriel
Herrero Simon, Ramon
Kurt, H.
Staliunas, Kestutis
Giden, I.
We propose for the first time a simple realization of a twodimensional ParityTime symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an antisymmetric gain/loss distribution on the same scale. That leads to nonreciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.

Suppression of modulation instability by spatiotemporal modulation
http://hdl.handle.net/2117/28105
Suppression of modulation instability by spatiotemporal modulation
Staliunas, Kestutis
Modulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatiotemporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerrnonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.
20150529T15:05:10Z
Staliunas, Kestutis
Modulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatiotemporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerrnonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.

Beam focusing in chirped mirror with a defect
http://hdl.handle.net/2117/27767
Beam focusing in chirped mirror with a defect
Cheng, Yu Chieh; Staliunas, Kestutis
Recently the beam focusing in reflection from chirped dielectric mirror has been proposed and demonstrated, where the negative (anomalous) diffraction is responsible for this flat mirror focusing. For a strong focusing performance (large focal distance), a wide angular range of strong (negative) angular dispersion is required. We show that a defect layer in the dielectric mirror (one layer is of a double size), can increase the angular dispersion, and thus improve the focusing performance. By introducing a defect layer in the chirped mirror, the focal distances can be increase from 12 µm up to 22 µm in a specific, calculated, structure, as our numerical integration show.
20150506T09:53:50Z
Cheng, Yu Chieh
Staliunas, Kestutis
Recently the beam focusing in reflection from chirped dielectric mirror has been proposed and demonstrated, where the negative (anomalous) diffraction is responsible for this flat mirror focusing. For a strong focusing performance (large focal distance), a wide angular range of strong (negative) angular dispersion is required. We show that a defect layer in the dielectric mirror (one layer is of a double size), can increase the angular dispersion, and thus improve the focusing performance. By introducing a defect layer in the chirped mirror, the focal distances can be increase from 12 µm up to 22 µm in a specific, calculated, structure, as our numerical integration show.